This invention relates generally to identification systems. Specifically, the present invention concerns identification systems which are useful in a battlefield environment. In this environment, an interrogator, such as a first tank, may wish to examine a target, such as a second tank, to determine whether the target represents a friend or foe. More specifically, the present invention relates to identification systems which minimize the possibility of detecting the presence or location of either the interrogator or target by unfriendly forces. Further, the present invention relates to identification systems which remain operative and secure in spite of jamming or capture by unfriendly forces.
An identification system in a battlefield environment can help reduce fratricide among friendly forces. Additionally, an identification system can increase firing rates by reducing the time spent deciding whether a target represents a friend or foe. An identification system typically provides only an indication of whether a target represents a friend or a foe. Typically, no drastic action, such as fire a gun, is automatically taken upon the receipt of this indication. Rather, the final denison concerning whether to take some action typically remains with a human operator. Thus, an identification system which identifies an interrogator or target to an enemy, is inoperative, susceptible to jamming, overly complicated, or is exploitable upon capture by the enemy, may not be used. Such an identification system becomes useless in reducing fratricide or increasing battlefield firing rates.
Various identification systems have been proposed. However these identification system tend to suffer serious drawbacks. One identification system requires an interrogator to transmit a relatively low frequency, radio frequency (RF) signal to which a friendly target responds by transmitting another RF signal. But, such low frequency transmitted RF signals may be easily received by an enemy as well as friends. This system can potentially identify the interrogator and the interrogator's position to enemy forces who are capable of receiving the interrogator's transmitted RF signal.
In other identification systems, targets reply to an interrogation by transmitting relatively long, secret codes. But, such reply codes may be relatively easy to detect by an enemy and become susceptible to jamming. Additionally, if the codes are known in advance, an enemy may be able to exploit the identification system.